Regarding the accuracy of mounting electronic components on electronic circuit boards, there has been a growing demand for increasing the accuracy with the minimization of electronic components to be mounted. In order to achieve the mounting accuracy as described above, various devices have conventionally been proposed. For example, a method for image-picking up board marks existing on the circuit board loaded into a component mounting apparatus by means of a board recognition camera to obtain the displacement of the circuit board, image-picking up, by means of a component recognition camera, the electronic component held by a suction nozzle of an X-Y robot that carries out component mounting by moving in the X- and Y-directions to obtain the displacement of the electronic component, correcting the displacements of both the board and the component, and then mounting the electronic component on the circuit board by means of the X-Y robot, and the like are disclosed. Furthermore, a method for further improving the mounting accuracy by obtaining relative positions between the suction nozzle of the X-Y robot, the board recognition camera, and the component recognition camera in addition to the method (see, for example, Japanese unexamined patent publication No. H08-242094) is also proposed.
Furthermore, since the X-Y robot is expanded and contracted due to a temperature change of the component mounting apparatus accompanying the operation of the component mounting apparatus that has the X-Y robot, a method for improving the mounting accuracy in consideration of the amount of expansion and contraction is also proposed. As shown in FIG. 28, the method image-picks up a reference mark 4 by means of a board recognition camera 3 attached to a head 2 provided for an X-Y robot 1 and obtains the displacement of the X-Y robot 1 due to heat on the basis of the image-pick up information (see, for example, Japanese unexamined patent publication No. H06-126671).
Although the various methods are proposed to improve the component mounting accuracy as described above, the advancement of the minimization of electronic components are remarkable, and the component mounting accuracy has become more severe in accordance with it. Therefore, it is a possible case that the aforementioned methods cannot satisfy the mounting accuracy of the recent electronic components. It is concretely currently demanded to mount, for example, a chip component of a size of 1.6×0.8 mm within an error range of, for example, ±70 μm.
Moreover, it is required to obtain the relative positional relation between the suction nozzle of the X-Y robot and the component recognition camera in order to improve the component mounting accuracy. However, it is not easy to obtain the relative positional relation since the X-Y robot expands and contracts due to heat as described above. That is, when the amount of expansion and contraction of the X-Y robot 1 due to heat is considered, if an X-axis robot 7 and Y-axis robots 8 that constitute the X-Y robot 1 are arranged perpendicular to each other and heat takes effect as shown in FIG. 28, it is possible to cope with the expansion and contraction so long as the X-Y robot 1 expands and contracts with the perpendicular state maintained. That is, if the expansion and contraction of the X-axis robot 7 and the Y-axis robots 8 occur only in one direction, it is possible to regard the amounts of expansion and contraction same or approximately equal to each other in a position where the reference mark 4 is image-picked up by a camera 3 provided for the head 2 to calculate the amount of expansion and contraction of the X-Y robot 1 and a position where the head 2 actually mounts an electronic component on the printed board 6, or calculate the amount of displacement in the placing position from the amount of the expansion and contraction at the reference mark image-pickup position, and it is possible to treat the amount of the expansion and contraction obtained on the basis of the image-pickup as effective.
However, conventionally, even when the placing position is corrected in consideration of the amount of expansion and contraction, it is true that the mounting accuracy cannot be improved to the intended extent. Although the reason for the above has not completely been clarified, it may be considered as the reason that the expansion and construction of the X-Y robot 1 occur not only in the X-axis direction and the Y-axis direction but also in other directions when heat takes effect in the conventional structure. That is, as exampled or illustrated with exaggeration in FIGS. 29 and 30, it can be considered that the X-axis robot 7 and the Y-axis robots 8 independently deform to expand, warp, or in a similar manner due to heat. Therefore, it can be considered that the amounts of expansion and construction as well as the displacement directions of the X-Y robot 1 are disadvantageously varied in the position where the reference mark 4 is image-picked up by the camera 3 provided for the head 2 to calculate the amount of expansion and contraction of the X-Y robot 1 and the position where the head 2 actually mounts the electronic component on the printed board 6, and the obtained amounts of expansion and contraction cannot contribute to the correction of the placing position, causing no improvement in the mounting accuracy.
Although the component mounting of component suction by the nozzle of the head, recognition by the camera of the sucked component, and placement on the board has been carried out by moving the component suction head in the X- and Y-directions by driving the X-Y robot, it has not been able to achieve high mounting accuracy due to the distortion of the component mounting apparatus itself no matter how the component recognition accuracy has been improved. The distortion of the component mounting apparatus itself is attributed to the poor machining accuracy or poor assembling accuracy of the X-Y robot of the component mounting apparatus.
If the impossibility of the high-accuracy component placing on the board during placing due to the distortion of the X-Y robot attributed to the factors of machining accuracy and so on as described above is analyzed more concretely, displacements in the X- and Y-directions are caused by the yawing (rolling in the direction perpendicular to the traveling direction of the head moving on the X-Y robot), pitching (poor linearity in the transfer pathway of the head), and rolling (pitching in a direction at an angle of ninety degrees different from the above rolling) of the guide members of the X-Y robot.
Accordingly, the component mounting has conventionally been made accurate by carrying out camera calibration, recognizing the reference mark of a reference board by means of a component recognition camera fixed to the X-Y robot, calculating the amount of displacement between a target position where the reference mark should properly exist and the actual position of the reference mark, and carrying out correction by adding the calculated amount of displacement as a placing position offset value to each position (see, for example, Japanese unexamined patent publication No. H06-126671).
In this case, the camera calibration of the board recognition camera is to make the board recognition camera recognize a jig of which the position coordinate is previously known in order to detect the installation error of the board recognition camera, calculate the installation error of the board recognition camera by a difference between the position coordinate calculated on the basis of the recognition result and the previously known position coordinate, and carry out positional correction. During the camera calibration, not only the positional correction of the board recognition camera but also the positional correction of the component recognition camera and the nozzle are additionally carried out.
However, according to the method of carrying out the correction in each of the positions, it is possible that the position of the reference board is displaced by, for example, almost 1 mm between the first-time positioning and the second-time positioning of the reference board. Furthermore, the reference board is very expensive since the reference board is required to have very high accuracy, and the positioning is achieved by stopping the reference board in an approximate X-direction position without using a board stopper from the viewpoint of the damage prevention. In addition, a board conveyor, which has a gap slightly smaller than 1 mm also in the Y-direction for conveyance, therefore has no reproducibility of the positioning of the reference board in the board holding section of the component mounting apparatus, and this becomes a factor that reduces the mounting accuracy.
As described above, the amounts of relative displacement between the respective positions of the robot are obtained by positioning the reference board in the approximate position and thereafter recognizing the reference mark of the reference board, and the amounts of displacement are reflected in the placing position data of the mounting board during mounting. This therefore is a factor that reduces the mounting accuracy.
On the other hand, in a case where the correction is carried out by recognizing a glass reference board provided with a grid in a matrix form, it can be considered to measure the grid of the reference board on the assumption that the reference board is accurately positioned and uses the measured data as a correction value without modification.
However, it is very difficult to accurately hold the reference board on the micrometer order in the board holding section as described above, and a special positioning device for accurately holding the board in the board holding section of the component mounting apparatus is necessary. Eventually, if the measured data is used directly as a correction value, it is impossible to accurately correct the X-Y robot unless the reference board is accurately positioned with high reproducibility.
If the component placing region of the component mounting apparatus is totally taken into consideration, there has been an issue that the mounting accuracy has not been able to be secured due to insufficient correction only by the conventional camera calibration and the placing position offset value for the reason that the distortion of the head operation due to the distortion of the X-Y robot has been changed depending on the position where positioning is carried out.
Even if the reference board itself on which a lot of reference marks are arranged at regular intervals in a matrix form can be accurately manufactured, it is impossible to provide an absolute parallel between the X-Y robot and the reference board. Furthermore, as a result that the absolute perpendicularity of the X-Y robot itself is not guaranteed, there is existing no reference. Since the X-Y robot, on which the head that has had the board recognition camera for recognizing the reference board arranged in the component placing region of the component mounting apparatus has been supported, has been distorted, the position obtained from the reference board has not been able to be used as a reference, and it has been unsuccessful to improve the placing accuracy (e.g., unsuccessful to increase the robot accuracy to about ±2 μm or increase the total accuracy of the mounting apparatus to about ±20 μm).
The present invention is made to solve the aforementioned issues and has an object to provide a component mounting apparatus and a component mounting method to be carried out by the component mounting apparatus which are capable of improving the component mounting accuracy further than in the conventional case.
Another object of the present invention is to solve the aforementioned issues and provide a component mounting method and apparatus which are capable of improving the placing accuracy by obtaining an optimum offset value in accordance with the size of the board.